Australian Prime Minister Tony Abbott said in early April that authorities were "very confident" the signals were coming from the plane's flight recorders, raising hopes of closure among some of the families of the 239 people on board the passenger jet.

But after spending weeks scouring the bottom of the ocean roughly 1,600 kilometers (1,000 miles) off Western Australia with a high-tech unmanned submarine, the searchers have drawn another blank, deepening the mystery surrounding the Boeing 777's fate.

Officials say they are still trying to figure out the source of the signals that led the search for the past seven weeks.

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The search for MH370 48 photos

The search for MH37048 photos

Relatives of passengers from Malaysia Airlines Flight MH370 console each other outside the Malaysia Airlines office in Subang, Malaysia, on Thursday, February 12. Protesters demanded that the airline withdraw the statement made in January that all the passengers aboard the plane are dead. The plane, which disappeared on March 8, has not been found.

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The search for MH37048 photos

A policewoman watches a couple whose son was on board the missing Malaysia Airlines Flight 370 cry outside the airline's office building in Beijing after officials refused to meet with them on June 11, 2014. The search for the missing plane has been ongoing since early 2014.

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Members of the media scramble to speak with Azharuddin Abdul Rahman, director general of Malaysia's Civil Aviation Department, at a hotel in Kuala Lumpur, Malaysia, on May 27, 2014. Data from communications between satellites and missing Malaysia Airlines Flight 370 was released the day before, more than two months after relatives of passengers say they requested that it be made public.

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Operators aboard the Australian ship Ocean Shield move Bluefin-21, the U.S. Navy's autonomous underwater vehicle, into position to search for the jet on April 14, 2014.

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A member of the Royal New Zealand Air Force looks out of a window while searching for debris off the coast of western Australia on April 13, 2014.

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The Echo moves through the waters of the southern Indian Ocean on April 12, 2014.

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A Royal Australian Air Force AP-3C Orion, on a mission to drop sonar buoys to assist in the search, flies past the Australian vessel Ocean Shield on April 9, 2014.

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A relative of a missing passenger cries at a vigil in Beijing on April 8, 2014.

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Australian Defense Force divers scan the water for debris in the southern Indian Ocean on April 7, 2014.

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A towed pinger locator is readied to be deployed off the deck of the Australian vessel Ocean Shield on April 7, 2014.

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A member of the Royal New Zealand Air Force looks at a flare in the Indian Ocean during search operations on April 4, 2014.

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A member of the Japanese coast guard points to a flight position data screen while searching for debris from the missing jet on April 1, 2014.

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On March 30, 2014, a woman in Kuala Lumpur prepares for an event in honor of those aboard Flight 370.

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A Royal New Zealand Air Force member launches a GPS marker buoy over the southern Indian Ocean on March 29, 2014.

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The sole representative for the families of Flight 370 passengers leaves a conference at a Beijing hotel on March 28, 2014, after other relatives left en masse to protest the Malaysian government's response to their questions.

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A member of the Royal Australian Air Force is silhouetted against the southern Indian Ocean during the search for the missing jet on March 27, 2014.

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Flight Lt. Jayson Nichols looks at a map aboard a Royal Australian Air Force aircraft during a search on March 27, 2014.

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People in Kuala Lumpur light candles during a ceremony held for the missing flight's passengers on March 27, 2014.

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Malaysian Prime Minister Najib Razak, center, delivers a statement about the flight on March 24, 2014. Razak's announcement came after the airline sent a text message to relatives saying it "deeply regrets that we have to assume beyond any reasonable doubt that MH 370 has been lost and that none of those onboard survived."

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Grieving relatives of missing passengers leave a hotel in Beijing on March 24, 2014.

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Ground crew members wave to a Japanese Maritime Defense Force patrol plane as it leaves the Royal Malaysian Air Force base in Subang, Malaysia, on March 23, 2014. The plane was heading to Australia to join a search-and-rescue operation.

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A passenger views a weather map in the departures terminal of Kuala Lumpur International Airport on March 22, 2014.

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A Chinese satellite captured this image, released on March 22, 2014, of a floating object in the Indian Ocean, according to China's State Administration of Science. It is a possible lead in the search for the missing plane. Surveillance planes are looking for two objects spotted by satellite imagery in remote, treacherous waters more than 1,400 miles from the west coast of Australia.

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Satellite imagery provided by the Australian Maritime Safety Authority on March 20, 2014, shows debris in the southern Indian Ocean that could be from Flight 370. The announcement by Australian officials that they had spotted something raised hopes of a breakthrough in the frustrating search.

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Another satellite shot provided by the Australian Maritime Safety Authority shows possible debris from the flight.

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A distraught relative of a missing passenger breaks down while talking to reporters at Kuala Lumpur International Airport on March 19, 2014.

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On March 18, 2014, a relative of a missing passenger tells reporters in Beijing about a hunger strike to protest authorities' handling of information about the missing jet.

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U.S. Navy crew members assist in search-and-rescue operations in the Indian Ocean on March 16, 2014.

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Members of the Chinese navy continue search operations on March 13, 2014. The search area for Flight 370 has grown wider. After starting in the sea between Malaysia and Vietnam, the plane's last confirmed location, efforts are expanding west into the Indian Ocean.

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A Vietnamese military official looks out an aircraft window during search operations March 13, 2014.

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Malaysian air force members look for debris near Kuala Lumpur on March 13, 2014.

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Relatives of missing passengers wait for the latest news at a hotel in Beijing on March 12, 2014.

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Indonesian air force officers in Medan, Indonesia, examine a map of the Strait of Malacca on March 12, 2014.

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A member of the Vietnamese air force checks a map while searching for the missing plane on March 11, 2014.

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Vietnam air force Col. Le Huu Hanh is reflected on the navigation control panel of a plane that is part of the search operation over the South China Sea on March 10, 2014.

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A Vietnamese air force plane found traces of oil that authorities had suspected to be from the missing Malaysia Airlines plane, the Vietnamese government online newspaper reported on March 8, 2014. However, a sample from the slick showed it was bunker oil, typically used to power large cargo ships, Malaysia's state news agency, Bernama, reported on March 10, 2014.

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A U.S. Navy Seahawk helicopter lands aboard the USS Pinckney to change crews on March 9, 2014, before returning to search for the missing plane in the Gulf of Thailand.

Italian tourist Luigi Maraldi, who reported his passport stolen in August, shows his current passport during a news conference at a police station in Phuket island, Thailand, on March 9, 2014. Iranians Pouri Nourmohammadi and Delavar Seyed Mohammad Reza were identified by Interpol as the two men who used stolen passports to board the flight. But there's no evidence to suggest either was connected to any terrorist organizations, according to Malaysian investigators. Malaysian police believe Nourmohammadi was trying to emigrate to Germany using the stolen Austrian passport.

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Vietnamese air force crew stand in front of a plane at Tan Son Nhat airport in Ho Chi Minh City on March 9, 2014, before heading out to the area between Vietnam and Malaysia where the airliner vanished.

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Buddhist monks at Kuala Lumpur International Airport offer a special prayer for the missing passengers on March 9, 2014.

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The Chinese navy warship Jinggangshan prepares to leave Zhanjiang Port early on March 9, 2014, to assist in search-and-rescue operations for the missing Malaysia Airlines flight. The Jinggangshan, an amphibious landing ship, is loaded with lifesaving equipment, underwater detection devices and supplies of oil, water and food.

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Members of a Chinese emergency response team board a rescue vessel at the port of Sanya in China's Hainan province on March 9, 2014. The vessel is carrying 12 divers and will rendezvous with another rescue vessel on its way to the area where contact was lost with Malaysia Airlines Flight 370.

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The rescue vessel sets out from Sanya in the South China Sea on March 9, 2014.

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Malaysian Prime Minister Najib Razak, center, arrives to meet family members of missing passengers at the reception center at Kuala Lumpur International Airport on March 8, 2014.

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A relative of two missing passengers reacts at their home in Kuala Lumpur on March 8, 2014.

Malaysia Airlines Group CEO Ahmad Juahari Yahya, front, speaks during a news conference at a hotel in Sepang on March 8, 2014. "We deeply regret that we have lost all contacts" with the jet, he said.

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EXPAND GALLERY

More than 11 weeks after Flight 370 dropped off radar screens over Southeast Asia on a scheduled flight to Beijing, officials in charge of the hunt are drawing a line through the ping-centered search and moving on to the next phase.

Where does the search go next?

The underwater search area guided by the pings covered more than 850 square kilometers (330 square miles). With that zone now ruled out, Australian authorities, who have been coordinating the search in the southern Indian Ocean, say attention will shift to a new area as large as 60,000 square kilometers.

That's roughly the size of West Virginia.

"The search will be a major undertaking," the Australian Transport Safety Bureau (ATSB) said this week. "The complexities and challenges involved are immense, but not impossible."

The underwater search will remain in the same overall region, as officials are basing their focus on an analysis of satellite, radar and other data that concludes the plane ended up somewhere along an arc stretching into the southern Indian Ocean.

"What has not changed at this stage is the belief that, after weeks of research and re-analysis, that the Inmarsat data is correct and that they are looking broadly in the right area," said Geoffrey Thomas, the editor in chief of Airlineratings.com, referring to the satellite data provided by the British company Inmarsat.

"Now clearly, we were hoping that the pings would narrow that broad area down to a narrow one, but that has not been the case, and now we have to unfortunately go the long road," Thomas told CNN.

Will they start searching the new area immediately?

No. In fact, it hasn't yet been fully mapped out.

The ATSB said this week that it's reviewing existing information from experts in order to refine the new zone.

Meanwhile, a specialized Chinese ship, the Zhu Kezhen, has begun mapping the ocean floor in some areas already picked out by the ATSB. A contracted commercial survey vessel will join those efforts next month.

It's unclear how deep the water is in these areas because "it's never been mapped," Australian Deputy Prime Minister Warren Truss said earlier this month. Officials say depths are likely to exceed 6,000 meters (20,000 feet).

The survey will take about three months and "give us crucial knowledge of the seafloor terrain needed to begin the underwater search," the ATSB said.

Who will do the actual searching?

That's still being figured out.

The Bluefin-21, the robotic submersible supplied by the U.S. Navy that has been searching the area where the pings were detected, has reached the end of its mission.

Search officials are regrouping and preparing to identify and deploy other high-tech equipment. But that's going to take some time -- up to two months, if not longer, according to Australian authorities.

Search coordinators say they are looking for sonar equipment that can be towed by a ship, an autonomous underwater vehicle with a mounted sonar device and optical imaging equipment.

Some towed sonar devices, such as the U.S. Navy's Orion, can transmit data to the surface in real-time. They also have the capability of scanning a larger area than the Bluefin, which was limited to about 40 square kilometers during each mission.

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Australian authorities say they plan to post their request for tenders for the next phase of the search in the coming days.

Who's going to pay for it?

That's another issue that isn't clear yet.

Australia has estimated the next phase of the search will cost $60 million, with the breakdown of exactly who's going to pay for what yet to be announced.

While 26 countries have participated in the hunt for the missing plane, Malaysia, China and Australia have held high-level talks about the future of the search.

Malaysia is where the plane is from, most of the people on the flight were Chinese, and Australia had six passengers on board and is closest to the remote part of the Indian Ocean where searchers have focused their hunt.

The United States has contributed a range of assets to the search so far, including the Bluefin-21, which costs an estimated $40,000 a day to operate.

Are the searchers still looking in the right place?

Australian officials say they remain confident in the conclusion -- reached by a team of experts from Boeing and aviation authorities around the world, including the United States and Europe -- that Flight 370 ended its journey in the southern Indian Ocean.

Despite questions from independent experts, Inmarsat says it stands by its analysis of a series of communications between the plane and the company's satellite system that provided a key part of the conclusion about the jetliner's path.

Earlier this week, Malaysian authorities released the satellite data from Inmarsat, meeting a long-standing request of some passengers' families who were unsatisfied by authorities' explanation of the plane's fate.